I'm familiar with normal lighting, T8's/T5's/CF's but new to the LED scene. Just got a Marineland LED fixture on a good package deal today and wanted to get more familiar on identifying the light ranges from low to high.

Whats considered low lighting and whats considered high?

Do plants thrive the same compared to a 6,700k bulb? I'm assuming hour duration's are the same?

There is no 'watts per gallon rule', that dosen't even work with fluorescents.

Unless they give some indication of the color spectrum (the kelvin rating) there isn't really much you can know. You can try googling your fixture for a "PAR" reading if someone else happened to test it. That could give you an idea. The amount of lumens might also give some kind of an indication. Lumens will tell you how much total light energy there is, but PAR tells you how much is useful for plants (plants only use a specific range of wavelengths).

But, yes, LEDs can come in a light spectrum like 6700K. I personally built my own fixture which uses 5665K LEDs.

I've no idea how they compare to fluorescents other than my plants grow great under them. In terms of lumens, my LED fixture is equivalent to a dual T8 fixture. That is, mine gives off 1400 lumens.

That page was only showing lux, which is the amount of lumens per square meter. It is still total light energy, and not just the specific wavelengths pertinent to plants.

It does however give an idea of how it compares to other fixtures. Looks like the marineland double bright is better than a single T8, but worse than a dual T8. If it's the regular LED fixture, I believe it's half the lumen value of the double. They still don't give color temperature though.

Im my experience, LEDs lack the penetration power of Florescent lighting. Even if the spectrum is right, if the light is diffusing too quickly, its not going to give your plants the power it needs. The choice of lighting is also dependent on what plants you are keeping and size of the tank. Shallow tanks will not need as powerful penetrating lights as deep tanks. Some plants will grow better under high light, others will turn clear and die under overly bright lights.